Tag Archives: Databases

When we write tests for our data access code, we must follow these three rules: Our tests must use the real database schema. Our tests must be deterministic. Our tests must assert the right thing. These rules are obvious. That is why it is surprising that some developers break them ...

Table-valued functions are an awesome thing. Many databases support them in one way or another and so does PostgreSQL. In PostgreSQL, (almost) everything is a table. For instance, we can write: CREATE OR REPLACE FUNCTION f_1 (v1 INTEGER, v2 OUT INTEGER) AS $$ BEGIN v2 := v1; END $$ LANGUAGE plpgsql; … ...

When performing database migrations, we at Data Geekery recommend using jOOQ with Flyway – Database Migrations Made Easy. In this post, we’re going to look into a simple way to get started with the two frameworks. Philosophy There are a variety of ways how jOOQ and Flyway could interact with each other in various development setups. In this ...

Types of primary keys All database tables must have one primary key column. The primary key uniquely identifies a row within a table therefore it’s bound by the following constraints: UNIQUE NOT NULL IMMUTABLE When choosing a primary key we must take into consideration the following aspects: the primary key may be used for joining other tables through a ...

You may have stumbled on this MySQL error. If you have already seen this before, then it’s really easy to recognize this and fix it. But if you haven’t seen this error before, then it takes a little longer to troubleshoot the issue. I am listing down the steps to troubleshoot this issue. ...

(Sorry for that click-bait heading. Couldn’t resist!) We’re on a mission. To teach you SQL. But mostly, we want to teach you how to appreciate SQL. You’ll love it! Getting SQL right or wrong shouldn’t be about that You’re-Doing-It-Wrong™ attitude that can be encountered often when evangelists promote their object of evangelism. Getting SQL right should be about the fun ...

Recently, an application that my team was working on encountered problems with a MySQL deadlock situation and it took us some time to figure out the reasons behind it. This application that we deployed was running on a 2-node cluster and they both are connected to an AWS MySQL database. The MySQL db tables are mostly based on InnoDB which ...

This post is a recap of the second day of Hbase from the Seven Databases in Seven Weeks book. Most of the commands and scripts can be found at GitHub: https://github.com/eyalgo/seven-dbs-in-seven-weeks/tree/master/hbase/day_2 Streaming Script The first thing in day 2 was to download lots of data (big data) and stream it into Hbase. There’s a JRuby script, which I had to ...

SQL Server is known to have a very strict interpretation of the SQL standard. For instance, the following expressions or statements are not possible in SQL Server: -- Get arbitrarily numbered row_numbers SELECT ROW_NUMBER() OVER () -- Skip arbitrary rows SELECT a FROM (VALUES (1), (2), (3), (4)) t(a) OFFSET 3 ...

Recently, at the office: Bob: I’ve looked into that slow query you’ve told me about yesterday, Alice. I’ve added the indexes you wanted. Everything should be fine now Alice: Thanks Bob. I’ll quickly check … Nope Bob, still slow, it didn’t seem to work Bob: You’re right Alice! It looks like Oracle isn’t picking up the index, for your query ...

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